The present invention relates to a fluid level regulating method and a fluid temperature regulator for an automatic transmission.
In an automatic transmission (AT) used for a vehicle, a torque converter and an auxiliary transmission mechanism are disposed, and “ATF” (automatic transmission fluid) is supplied as hydraulic fluid into these devices.
If the automatic transmission continues to be driven, there is a possibility that gears or the like forming the transmission are shaved to mix impurities into the hydraulic fluid, thereby reducing responsivity of the automatic transmission. Moreover, deterioration of the hydraulic fluid itself may reduce durability of a clutch and the like. Therefore, it is necessary to periodically change hydraulic fluid and to add a proper amount of hydraulic fluid again. In this case, however, a proper amount of hydraulic fluid needs to be ensured when the automatic transmission is actuated and therefore a fluid level of the hydraulic fluid needs to be regulated after the hydraulic fluid has been distributed inside the torque converter and the auxiliary transmission mechanism. Therefore, in a technique described in Japanese Laid-open Patent Application No. 11-325235, for example, fluid level regulation is carried out while keeping the engine at idle.
However, if the hydraulic fluid regulation is carried out while keeping the engine at idle in this manner, the temperature of the hydraulic fluid rises as the hydraulic fluid is changed to cause thermal expansion of the hydraulic fluid. Moreover, a rise in the temperature of the hydraulic fluid during the fluid level regulation varies widely depending on various configurations of the internal combustion engine and the automatic transmission. If the temperature of the hydraulic fluid rises excessively, an increase in the volume of the hydraulic fluid due to thermal expansion becomes large and the hydraulic fluid after the regulation may actually be insufficient. Therefore, it is difficult to accurately carry out the fluid level regulation of the hydraulic fluid while keeping the engine at idle.